The overall goals of our research program are to better understand how Epstein-Barr virus (EBV) successfully infects humans, how it causes human disease, and to develop effective therapies against EBV-associated disease. This competing renewal builds on our progress in both macaque and human systems to study EBV infection in the context of the complete host. In the rhesus macaque animal model for EBV infection, we have constructed the first molecular clone for the EBV-related lymphocryptovirus that naturally infects rhesus macaques (rhLCV). Experimental infection with a rhLCV carrying a truncated rhBARF1, a putative immune evasion gene, has revealed a potential role for this viral protein in both acute and persistent infection. In the current proposal, we will use this animal model system to better understand how viral immune evasion contributes to the pathogenesis of acute and persistent LCV infection in a natural host. In humans with EBV-associated Nasopharyngeal Carcinoma (NPC), we have identified a functional defect in EBNA-1-specific cytotoxic T cells (CTL) that may represent an important hole in immunosurveillance against this virus-induced malignancy. Understanding how viral immunity is altered in patients with malignant EBV infection can be directly translated into significant improvements for cancer immunotherapy. The specific aims of this proposal are as follows: Specific Aim 1: Determine the role of rhBARF1 in acute and persistent rhLCV infection, Specific Aim 2: Determine the role of rhEBNA-1 CTL and potential rhEBNA-1 immune evasion in persistent rhLCV infection, Specific Aim 3: Determine the mechanism of EBNA-1 CTL inhibition in patients with EBV- associated Nasopharyngeal Carcinoma in order to develop strategies for improving EBNA-1 CTL activity for immunotherapy. These studies will provide new information on how EBV establishes persistent infection and how the immune response can be used to more effectively treat EBV-associated malignancy.